Example of middleware for heroku forwarding

ip.py

class ReverseProxy(object):
    def process_request(self, request):
        unsafe = True
        try:
            forwarded_for_split = [x.strip() for x in request.META['HTTP_X_FORWARDED_FOR'].split(',')]
            # Client connecting to heroku’s stuff is the last listed one.
            # http://stackoverflow.com/q/18264304/429091
            request.META['REMOTE_ADDR'] = forwarded_for_split.pop()
            unsafe = False
        except KeyError:
            pass
        except IndexError:
            pass

        if unsafe:
            raise Exception(
                'You are attempting to use middleware for X-Forwarded-For in an environment'
                + ' which does not set X-Forwarded-For. This means that your server will *only*'
                + ' ever accept spoofed IPs. This configuration intentionally throws an exception'
                + ' because silently “handling” the error would be very insecure.')
        # Fake out forwarded for by setting it to the remaining or unsetting if empty
        if forwarded_for_split:
            request.META['HTTP_X_FORWARDED_FOR'] = forwarded_for_split.join(',')
        else:
            del request.META['HTTP_X_FORWARDED_FOR']